My goal is to understand the genetic and molecular basis of determination and positional information. I propose to analyze these phenomena in the imaginal discs of Drosophila, because a great deal is already known about disc development and they are an extremely convenient source of material. I propose to analyze determination by studying homoeotic mutations of the bithorax complex that cause a segmental transformations in the thorax and abdomen of Drosophila. By the appropriate in vivo culture experiments I will determine what aspects of the determination system has been altered by various mutations. By the use of high resolution two-dimensional gel electrophoresis and the unique properties of tissue transformed by a mutation which I have previously studied. I hope to identify the protein or proteins involved in metathoracic determination. I propose to develop an assay system for the study of the biochemical basis of positional information. Preliminary experiments indicate that metabolically dead tissue can induce regeneration in a test fragment of an imgainal disc with which it is grafted. Using this method (or a similar one using dissociated and then reaggregated disc cells) I propose to determine what chemical modifications destroy the ability of tissue to induce regeneration in the test fragment. I also propose to study regional biochemical differences within discs using high resolution, two-dimensional gel electrophoresis and lectins and to try to correlate these results with what is known about the positional information fields in imaginal discs.